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Full text of "Handbook Of Chemical Engineering - I"

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POWER GENERATION AND TRANSMISSION
31
steam and one for maintaining the vacuum (dry air pump).   Condensers with tail pipes must be placed 35 to 40 ft. above the tail-water level.
Centrifugal air pumps, lately introduced, use the centrifugal action of water to entrain the air. They are simple in operation, though of low efficiency from a power standpoint. The Parsons Vacuum Augmenter uses a steam jet to draw out the air which is then passed over the coils of a small auxiliary condenser. The condensed steam is pumped out in the usual way, but by a pump which need not maintain the high vacuum existing in the condenser, and may there-ore be small.
The power required by condenser auxiliaries may vary from 1 to 10 per cent of the main engine output. It rarely pays to attempt better vacuums than 28 and 26 in. for turbines and engines respectively.
Cooling towers and cooling ponds are used where there is a scant supply of circulating water. The vacuum is usually poor and the cost of obtaining it relatively high.
Draft Apparatus.—The draft of a chimney varies directly as its height above the grates.   The volume of gas it discharges varies directly as the area, and as the square root of the height.   Very low and very high chimneys are both undesirable.   For sizes required, see the accompanying tables. The table gives the horsepower of chimneys computed by Kent method:
Diameter, inches	Height								Effective area, square feet	Actual area, square feet
	60 ft.	80 ft.	100 ft.	125 ft.	150 ft.	200 ft.	250 ft.	300 ft.		
18	25	29	30	36	40	46	51	56	0.97	1.77
24	54	62	69	78	85	98	110	120	2.08	3.14
30	92	107	119	133	146	169	189	206	3.58	4.91
36	141	163	182	204	223	258	288	315	5.47	7.07
42	200	231	258	289	316	365	408	447	7.76	9.62
48	269	311	348	389	426	492	549	602	10.44	12.57
60	437	505	565	632	692	800	894	979	16.98	19.64
72	646	747	835	934	1,023	1,181	1,320	1,447	25.08	28.27
84	896	1,035	1,157	1,294	1,418	1,637	1,830	2,005	34.76	38.48
96	1,186	1,370	1,532	1,713	1,876	2,167	2,423	2,654	46.01	50.27
108	1,517	1,751	1,959	2,054	2,392	2,770	3,098	3,393	58.83	63.62
120		2,180	2,438	2,557	2,986	3,448	3,855	4,223	73.22	78.54
132		2,656	2,970	3,114	3,637	4,200	4,696	5,144	89.18	95.03
144			3,554	3,726	4,352	5,027	5,618	6,155	106.72	113.10
168			4,878	5,115	5,974	6,899	7,713	8,449	146.50	153.94
192				6,724	7,852	9,068	10,138	11 , 105	192.56	201 . 06
216	i				9,987	11,532	12,894	H,123	244.90	254.47
240	..... ! .....				12,378	14,293	15,980	17,505	303.53	314.16
										
For pounds coal burned per hour for any given size of chimney, multiply figures in table by five. Chimneys 25 per cent larger are recommended for low-grade bituminous coal in middle and western states.
Chimney design must be based upon kind of coal required.    For overfeed stokers